Insufficient sleep is a major health and safety problem for young and older adults alike. National polls[unreadable] indicate that more than a quarter of adults 18-84 years of age regularly sleep less than 7 h per night, with[unreadable] 15% reporting sleeping less than 6 h per night. The deficits in alertness and performance ability associated[unreadable] with insufficient sleep can lead to greater risk for automobile accidents, home and workplace accidents, and[unreadable] on-the-job errors in sleepy individuals. Insufficient sleep can also have a negative effect on the quality of life,[unreadable] with impacts on irritability, mood, and motivation. There is evidence from acute sleep deprivation studies that[unreadable] older adults may respond differently to sleep loss than young adults, but studies comparing the response to[unreadable] chronic sleep restriction in older and young adults have not yet been conducted.[unreadable] Here, we propose to investigate the consequences of 4 weeks of chronic insufficient sleep on daytime[unreadable] alertness and performance in older (55-70) and young (18-30) adults. Subjects will be scheduled to sleep an[unreadable] equivalent of 5 h per 24 h in a forced desynchrony protocol, in order that we can investigate both the[unreadable] circadian and wake-dependent contributions to alertness and performance across the 4 weeks of sleep[unreadable] restriction. We will use subjective and objective measures to assess alertness across each waking episode,[unreadable] and subjects will perform a battery of tasks several times per day to measure the consequences of sleep[unreadable] restriction on cognitive throughput, sustained attention, reaction time, motivation, mood and short-term[unreadable] memory. Our study design will allow us to assess independently the impact of time-of-day (circadian phase)[unreadable] and duration of prior wakefulness, as well as their interactions, on measures of daytime alertness and[unreadable] performance under conditions of sleep restriction across 4 weeks.[unreadable] Results from this study have important implications for understanding the consequences of chronic[unreadable] insufficient sleep in older adults. Most adults regularly fail to get sufficient sleep, but few studies have[unreadable] attempted to quantify the consequences of chronic insufficient sleep in middle-aged and older people.[unreadable] Insufficient sleep can have important effects on health, safety, and quality of life. Knowledge of how the[unreadable] alertness, performance, and memory of healthy older people respond to insufficient sleep will provide a basis[unreadable] for future research and for advice and recommendations for maintaining health and well-being as we age.